[1]Dhātu. Data, (component, component part, but this is 'information' not 'object'), aspect, property, characteristic, whatever word you use, it means the basic categories into which things are divided for purposes of description. There is a danger in the use of the term 'element', the translation of Mrs. Rhys Davids and Bhk. Bodhi, in that this term implies the actual existance of a basic thing [the so-called 'ultimate' realities of the Abhidhamma, and DSG fanatics for example make this error] where what is being addressed is the information being received at the senses. If all eye-data were of an 'ultimate' nature, elemental, all eye consciousness of all visible objects would be the same [a uniform mass of light; rupa] at all times for all beings, and we know from experience that this is not the case.

[2]Nānatta. The this and that. In the Mulapariyaya, MN 1, the view following  higher, more refined, more detached than  ekatta (unity, all is one, "I am everything, everything is me") and preceding endlessness (or more usually The All) and Nibbana) with which one can mistakenly identify as self, as one's own, as a product of one's self or as the precurser to one's self. "You always want to be the one and only, and always end as only one of many."PED: Nānatta (nt. m.) [Sanskrit nānatva; abstr. from nānā] diversity, variety, manifoldness, multiformity, distraction; all sorts of (opp. ekatta, cp. M I.364: "the multiformity of sensuous impressions," M.A.). Enumn of diversity as nānattā, viz. dhātu- phassa- vedanā- saññā- sankappa- chanda- pari'āha- pariyesanā- lābha- D III.289; S II.140 sq., cp. IV.113 sq., 284 sq.; Ps I.87. - A IV.385; Ps I.63 sq., 88 sq.; S II.115 (vedanā-); Ps I.91 (samāpatti- and vihāra-); J II.265. In composition, substituted sometimes for nāna. Cp. Dialogues I.14, n. 2.
Nānā (adv.) [Ved. nānā, a redupl. nā (emphatic particle, see na1) "so and so," i. e. various, of all kinds] variously, differently.

[5]Dhammadhātu. There is no real legitimate way around this. Rhys Davids 'ideas' and Bhk. Bodhi's 'mental phenomena' both rely on deduction from the connection to mind-data interpreting mind-data in the usual western understanding; that is, anything that is not matter. This unwarrantedly excludes too much! The word means any 'thing' that has come into existance including material things. And taking a quick peek, you will note for yourself that material things are not omitted by the perceptions available to the mind. The mind is occupied with things. Any thing that has come into existence. Period. Eye consciousness is a product of the contact of a visible object with a working eye in connection with consciousness; the mind, taking eye-consciousness together with the other sense data consciousnesses, puts together our picture of the world.

[6] This is consistant with the idea of 'The All': The eye and sights, the ear and sounds, the nose and scents, the tongue and tastes, the body and touch, the mind and things.